Golf ball

ABSTRACT

An object of the present invention is to provide a golf ball having excellent spin performance on approach shots under a wet condition and excellent spin performance on approach shots under a condition that there is grass between the golf ball and the club face. The present invention provides a golf ball comprising a golf ball body and a paint film composed of at least one layer and formed on a surface of the golf ball body, wherein an outermost layer of the paint film located at the outermost layer of the golf ball contains a base resin and a porous filler, the base resin contains a polyurethane obtained by a reaction between a polyisocyanate composition and a polyol composition, and the porous filler contains SiO2 in an amount of 50 mass % or more as a constituent component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.16/818,653 filed on Mar. 13, 2020 now U.S. Pat. No. 11,235,203, whichclaims the priority benefit under 35 U.S.C. 119(a) to Japanese PatentApplication Nos. 2019-192019 filed on Oct. 21, 2019, and 2019-060595filed on Mar. 27, 2019, all of which are hereby expressly incorporatedby reference into the present application.

FIELD OF THE INVENTION

The present invention relates to a golf ball comprising a paint film.

DESCRIPTION OF THE RELATED ART

Conventionally, a golf ball has a paint film formed on a surface of agolf ball body. The paint film contributes to the performance, quality,appearance and the like of the golf ball. Regarding the performance ofthe golf ball of them, the paint film is considered to mainly contributeto the performance on a weak shot such as an approach shot because thepaint film is generally very thin in the thickness thereof.

It has been investigated to improve the performance of the golf ball bychanging the composition of the paint film. For example, JP 2015-503400A discloses a golf ball comprising a core and a cover substantiallysurrounding the core, wherein the cover includes at least one dimple andat least one land area adjacent to the at least one dimple, a portion ofthe surface of the golf ball is hydrophobic, and a portion of thesurface of the golf ball is hydrophilic.

JP 2013-521870 A discloses a golf ball comprising a golf ball bodyhaving an outer surface including a plurality of dimples formed thereon;and a protective coating applied to the outer surface of the golf ballbody and containing a hydrophobic thermoplastic polyurethane. Inaddition, JP 2001-214131 A discloses a golf ball clear paint containingan organic silicon compound.

SUMMARY OF THE INVENTION

However, the prior golf balls do not necessarily have satisfactory spinperformance on approach shots, and there is still room for improvementin the spin performance on approach shots under a wet condition. Inaddition, in the prior arts, the spin performance on approach shotsunder a condition that there is grass between the golf ball and the clubface was not investigated.

The present invention has been made in view of the abovementionedcircumstances, and an object of the present invention is to provide agolf ball having excellent spin performance on approach shots under awet condition and excellent spin performance on approach shots under acondition that there is grass between the golf ball and the club face.

The present invention that has solved the above problem provides a golfball comprising a golf ball body and a paint film composed of at leastone layer and formed on a surface of the golf ball body, wherein anoutermost layer of the paint film located at the outermost layer of thegolf ball contains a base resin and a porous filler, the base resincontains a polyurethane obtained by a reaction between a polyisocyanatecomposition and a polyol composition, and the porous filler containsSiO₂ in an amount of 50 mass % or more as a constituent component.

According to the present invention, a golf ball having excellent spinperformance on approach shots under a wet condition and excellent spinperformance on approach shots under a condition that there is grassbetween the golf ball and the club face is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cutaway cross-sectional view of a golf ballaccording to one embodiment of the present invention;

FIG. 2 is a schematic enlarged view showing a part of the golf ball ofFIG. 1 ;

FIG. 3 is a schematic cross-sectional view illustrating a measuringlocation of a thickness of a paint film; and

FIG. 4 is a schematic cross-sectional view illustrating a measuringlocation of a thickness of a paint film.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a golf ball comprising a golf ball bodyand a paint film composed of at least one layer and formed on a surfaceof the golf ball body, wherein an outermost layer of the paint filmlocated at the outermost layer of the golf ball contains a base resinand a porous filler, the base resin contains a polyurethane obtained bya reaction between a polyisocyanate composition and a polyolcomposition, and the porous filler contains SiO₂ in an amount of 50 mass% or more as a constituent component.

(Porous Filler)

First, the porous filler contained in the outermost layer of the paintfilm of the golf ball according to the present invention will beexplained. The porous filler has many fine pores. The shape of the finepore included in the porous filler is not particularly limited. The poresize of the fine pore included in the porous filler is not particularlylimited, but the pore size of the fine pore preferably ranges from 0.1nm to 500 nm. The pore size of the fine pore included in the porousfiller varies depending on the type of the porous filler. For example,zeolite has a pore size in a range from 0.1 nm to 2 nm, and diatomaceousearth has a pore size of about 300 nm.

The porous filler contains SiO₂ in an amount of 50 mass % or more as aconstituent component. If the amount of SiO₂ in the porous filler is 50mass % or more, the paint film has improved water repellency, and thusthe spin performance on the shot in a state wetted with water isimproved. The amount of SiO₂ in the constituent component of the porousfiller is preferably 55 mass % or more, more preferably 60 mass % ormore, and is 100 mass % or less, preferably 95 mass % or less, morepreferably 90 mass % or less. It is noted that the amount of SiO₂ wasdetermined by quantifying the amount of Si element by fluorescence X-rayanalysis and converting the amount of Si element into the amount of SiO₂component.

Examples of the porous filler include diatomaceous earth, zeolite andperlite. Diatom is a kind of plankton, and dead bodies of diatomdeposited on seabed or lake bed, and fossilized into Diatomaceous earth.Diatomaceous earth primarily contains silica, and has many very finestructures in each particle thereof. Perlite is a porous material formedwhen water included in a glassy volcanic stone such as obsidian,pearlstone and pitchstone is evaporated by treating the glassy volcanicstone at a high temperature. Zeolite is a crystalline porousalumino-silicate. Examples of the structure of zeolite include type A,ferrierite, ZSM-5, mordenite, beta, type X and type Y. It is noted thatzeolite also includes porous silicalite. The porous filler may be usedsolely, or two or more of them may be used in combination.

The volume average particle size of the porous filler is preferably 0.5μm or more, more preferably 1.0 μm or more, and even more preferably 2.0μm or more, and is preferably 30 μm or less, more preferably 20 μm orless, and even more preferably 15 μm or less. If the volume averageparticle size of the porous filler is 0.5 μm or more, thewater-discharging effect is better and the spin performance under a wetcondition is further enhanced, and if the volume average particle sizeof the porous filler is 30 μm or less, the appearance is better and thestain attachment can be decreased.

The bulk density of the porous filler is not particularly limited, butit is preferably 0.2 g/cm³ or more, more preferably 0.3 g/cm³ or more,and is preferably 1.0 g/cm³ or less, more preferably 0.9 g/cm³ or less,and even more preferably 0.8 g/cm³ or less.

The amount of the porous filler in the outermost layer of the paint filmis preferably 3 parts by mass or more, more preferably 5 parts by massor more, and even more preferably 8 parts by mass or more, and ispreferably 200 parts by mass or less, more preferably 150 parts by massor less, and even more preferably 120 parts by mass or less, withrespect to 100 parts by mass of the base resin of the outermost layer ofthe paint film. If the amount of the porous filler is 3 parts by mass ormore, the water-discharging effect is better and the spin performanceunder a wet condition is further enhanced, and if the amount of theporous filler is 200 parts by mass or less, the appearance is better andthe stain attachment is reduced.

(Polyurethane)

The base resin of the outermost layer of the paint film of the golf ballaccording to the present invention contains a polyurethane obtained by areaction between a polyisocyanate composition and a polyol composition.The outermost layer of the paint film is preferably formed from a paintcontaining the polyol composition and the polyisocyanate composition.Examples of the paint include a so-called two-component curing urethanepaint having the polyol composition as a base material and thepolyisocyanate composition as a curing agent.

(Polyol Composition)

The polyol composition contains a polyol compound. Examples of thepolyol compound include a compound having two or more hydroxyl groups inone molecule. Examples of the polyol compound include a compound havinga hydroxyl group at a terminal of the molecule, and a compound having ahydroxyl group at a portion other than the terminal of the molecule. Thepolyol compound may be used solely or as a mixture of at least two ofthem.

Examples of the compound having the hydroxyl group at the terminal ofthe molecule include a low molecular weight polyol having a molecularweight of less than 500 and a high molecular weight polyol having anaverage molecular weight of 500 or more. Examples of the low molecularweight polyol include a diol such as ethylene glycol, diethylene glycol,triethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol,and 1,6-hexanediol; and a triol such as glycerin, trimethylolpropane,and hexanetriol. Examples of the high molecular weight polyol include apolyether polyol, a polyester polyol, a polycaprolactone polyol, apolycarbonate polyol, a urethane polyol, and an acrylic polyol. Examplesof the polyether polyol include polyoxyethylene glycol (PEG),polyoxypropylene glycol (PPG), and polyoxytetramethylene glycol (PTMG).Examples of the polyester polyol include polyethylene adipate (PEA),polybutylene adipate (PBA), and polyhexamethylene adipate (PHMA).Examples of the polycaprolactone polyol include poly-ε-caprolactone(PCL). Examples of the polycarbonate polyol include polyhexamethylenecarbonate.

The urethane polyol is a compound having a plurality of urethane bondsin the molecule and having two or more hydroxyl groups in one molecule.Examples of the urethane polyol include a urethane prepolymer obtainedby a reaction between a first polyol component and a firstpolyisocyanate component under a condition that the amount of hydroxylgroups in the first polyol component is excessive to the amount ofisocyanate groups in the first polyisocyanate component.

Examples of the first polyol component of the urethane polyol include apolyether diol, a polyester diol, a polycaprolactone diol, and apolycarbonate diol, and the polyether diol is preferable. Examples ofthe polyether diol include polyoxyethylene glycol, polyoxypropyleneglycol, and polyoxytetramethylene glycol. Among them,polyoxytetramethylene glycol is preferable.

The number average molecular weight of the polyether diol is preferably500 or more, more preferably 600 or more, and is preferably 4,000 orless, more preferably 3,500 or less, even more preferably 3,000 or less.If the number average molecular weight of the polyether diol is 500 ormore, the distance between crosslinking points in the paint film becomeslong and the paint film becomes soft, thus the spin performance isenhanced. If the number average molecular weight of the polyether diolis 4,000 or less, the distance between crosslinking points in the paintfilm does not become excessively long, and thus the stain resistance ofthe paint film becomes better. It is noted that the average molecularweight of the polyol component can be measured, for example, by gelpermeation chromatography (GPC), using polystyrene as a standardmaterial, tetrahydrofuran as an eluate, and an organic solvent systemGPC column (e.g. “Shodex (registered trademark) KF series” availablefrom Showa Denko K.K.) as a column.

The first polyol component may include a low molecular weight polyolhaving a molecular weight of less than 500. Examples of the lowmolecular weight polyol include a diol such as ethylene glycol,diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol,neopentyl glycol, and 1,6-hexanediol, and a triol such as glycerin,trimethylolpropane, and hexanetriol. The low molecular weight polyol maybe used solely or as a mixture of at least two of them.

The urethane polyol preferably includes the triol component and the diolcomponent as the first polyol component. As the triol component,trimethylolpropane is preferable. The mixing ratio of the triolcomponent to the diol component (triol component/diol component) ispreferably 1.0 or more, more preferably 1.2 or more, and is preferably2.6 or less, more preferably 2.4 or less, in a molar ratio of OH group.

The first polyisocyanate component constituting the urethane polyol isnot particularly limited, as long as the first polyisocyanate componenthas at least two isocyanate groups. Examples of the first polyisocyanatecomponent include an aromatic polyisocyanate such as 2,4-tolylenediisocyanate, 2,6-tolylene diisocyanate, a mixture of 2,4-tolylenediisocyanate and 2,6-tolylene diisocyanate (TDI), 4,4′-diphenylmethanediisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI),3,3′-bitolylene-4,4′-diisocyanate (TODD, xylylene diisocyanate (XDI),tetramethylxylylenediisocyanate (TMXDI), and para-phenylene diisocyanate(PPDI); and an alicyclic polyisocyanate or aliphatic polyisocyanate suchas 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrogenatedxylylenediisocyanate (H₆XDI), hexamethylene diisocyanate (HDI),isophorone diisocyanate (IPDI), and norbornene diisocyanate (NED). Thesepolyisocyanates may be used solely or as a mixture of at least two ofthem.

The amount of the polyether diol in the urethane polyol is preferably 70mass % or more, more preferably 72 mass % or more, and even morepreferably 75 mass % or more. The polyether diol forms a soft segment inthe paint film. Thus, if the amount of the polyether diol is 70 mass %or more, the obtained golf ball has further enhanced spin performance.

The weight average molecular weight of the urethane polyol is preferably5,000 or more, more preferably 5,300 or more, and even more preferably5,500 or more, and is preferably 20,000 or less, more preferably 18,000or less, and even more preferably 16,000 or less. If the weight averagemolecular weight of the urethane polyol is 5,000 or more, the distancebetween crosslinking points in the paint film becomes long and the paintfilm becomes soft, thus the spin performance is enhanced. If the weightaverage molecular weight of the urethane polyol is 20,000 or less, thedistance between crosslinking points in the paint film does not becomeexcessively long, and thus the stain resistance of the paint filmbecomes better.

The hydroxyl value of the urethane polyol is preferably 10 mgKOH/g ormore, more preferably 15 mgKOH/g or more, and even more preferably 20mgKOH/g or more, and is preferably 200 mgKOH/g or less, more preferably190 mgKOH/g or less, and even more preferably 180 mgKOH/g or less. It isnoted that the hydroxyl value can be measured according to JIS K 1557-1,for example, by an acetylation method.

Examples of the compound having the hydroxyl group at the part otherthan the terminal of the molecule include a polyrotaxane having ahydroxyl group, and a hydroxyl group modified vinyl chloride-vinylacetate copolymer.

The polyrotaxane having the hydroxyl group has a cyclodextrin, a linearmolecule piercing through the cyclic structure of the cyclodextrin, andblocking groups located at both terminals of the linear molecule toprevent disassociation of the cyclic molecule. The polyrotaxane isviscoelastic, since the cyclodextrin molecule is movable along thelinear molecule that penetrates the cyclodextrin in a skewering manner(pulley effect). Even if a tension is applied to the polyrotaxane, thetension can be uniformly dispersed due to the pulley effect. Thus, thepolyrotaxane has an excellent property that a crack or scratch veryhardly occurs, unlike a conventional crosslinked polymer.

The cyclodextrin is a general term for an oligosaccharide having acyclic structure. The cyclodextrin is, for example, a molecule having 6to 8 D-glucopyranose residues being linked in a cyclic shape via anα-1,4-glucoside bond. Examples of the cyclodextrin includeα-cyclodextrin (number of glucose units: 6), β-cyclodextrin (number ofglucose units: 7), and γ-cyclodextrin (number of glucose units: 8), andα-cyclodextrin is preferable. As the cyclodextrin, one type may be usedsolely, and two or more types may be used in combination.

The linear molecule is not particularly limited, as long as it is alinear molecule capable of piercing through the cyclic structure of thecyclodextrin so that the cyclic structure of the cyclodextrin is movablealong and rotatable around the linear molecule. Examples of the linearmolecule include polyalkylene, polyester, polyether, and polyacrylicacid. Among them, polyether is preferable, and polyethylene glycol isparticularly preferable. Polyethylene glycol has less steric hindrance,and thus can easily pierce through the cyclic structure of thecyclodextrin in a skewering manner.

The weight average molecular weight of the linear molecule is preferably5,000 or more, more preferably 6,000 or more, and is preferably 100,000or less, more preferably 80,000 or less.

The linear molecule preferably has functional groups at both terminalsthereof. When the linear molecule has the functional group, the linearmolecule can easily react with the blocking group. Examples of thefunctional group include a hydroxyl group, a carboxyl group, an aminogroup, and a thiol group.

The blocking group is not particularly limited, as long as the blockinggroup is located at both terminals of the linear molecule to prevent thedisassociation of the cyclodextrin from the linear molecule. Examples ofthe method for preventing the disassociation include a method of using abulky blocking group to physically prevent the disassociation, and amethod of using an ionic blocking group to electrostatically prevent thedisassociation. Examples of the bulky blocking group include acyclodextrin and an adamantyl group. The number of the cyclodextrinskept by the linear molecule (kept amount) preferably ranges from 0.06 to0.61, more preferably ranges from 0.11 to 0.48, and even more preferablyranges from 0.24 to 0.41, if the maximum kept amount thereof is deemedas 1. This is because if the number is less than 0.06, the pulley effectmay not be exerted, and if the number exceeds 0.61, the cyclodextrinsare very densely located, so that the movability of the cyclodextrin maydecrease.

As the polyrotaxane, a polyrotaxane having at least a part of hydroxylgroups of the cyclodextrin being modified with a caprolactone chain, ispreferred. Modifying with the caprolactone alleviates the sterichindrance between the polyrotaxane and the polyisocyanate, therebyenhancing the reaction efficiency with the polyisocyanate.

As the above modification, for example, the hydroxyl groups of thecyclodextrin are treated with propylene oxide to hydroxylpropylate thecyclodextrin, and then ε-caprolactone is added to perform ring-openingpolymerization. As a result of this modification, the caprolactone chain—(CO(CH₂)₅O)_(n)H (n is a natural number of 1 to 100) is linked to theexterior side of the cyclic structure of the cyclodextrin via a—O—C₃H₆—O— group. “n” represents the degree of polymerization, and ispreferably a natural number ranging from 1 to 100, more preferably anatural number ranging from 2 to 70, and even more preferably a naturalnumber ranging from 3 to 40. At another terminal of the caprolactonechain, a hydroxyl group is formed through the ring-openingpolymerization. The terminal hydroxyl group of the caprolactone chaincan react with the polyisocyanate.

The ratio of the hydroxyl groups modified with the caprolactone chain toall the hydroxyl groups (100 mole %) included in the cyclodextrin beforethe modification is preferably 2 mole % or more, more preferably 5 mole% or more, even more preferably 10 mole % or more. If the ratio of thehydroxyl groups modified with the caprolactone chain falls within theabove range, the hydrophobicity of the polyrotaxane increases, and thereactivity with the polyisocyanate increases.

The hydroxyl value of the polyrotaxane is preferably 10 mg KOH/g ormore, more preferably 15 mg KOH/g or more, even more preferably 20 mgKOH/g or more, and is preferably 400 mg KOH/g or less, more preferably300 mg KOH/g or less, even more preferably 220 mg KOH/g or less,particularly preferably 180 mg KOH/g or less. If the hydroxyl value ofthe polyrotaxane falls within the above range, the reactivity with thepolyisocyanate increases, and thus the durability of the paint filmbecomes more favorable.

The total molecular weight of the polyrotaxane is preferably 30,000 ormore, more preferably 40,000 or more, and even more preferably 50,000 ormore, and is preferably 3,000,000 or less, more preferably 2,500,000 orless, and even more preferably 2,000,000 or less, in a weight averagemolecular weight. If the weight average molecular weight is 30,000 ormore, the paint film has sufficient strength, and if the weight averagemolecular weight is 3,000,000 or less, the paint film has sufficientflexibility and thus approach performance of the golf ball increases. Itis noted that the weight average molecular weight of the polyrotaxanecan be measured, for example, by gel permeation chromatography (GPC)using polystyrene as a standard substance, tetrahydrofuran as an eluant,and an organic solvent system GPC column (e.g., “Shodex (registeredtrademark) KF series” available from Showa Denko K.K.) as a column.

Specific examples of the polyrotaxane modified with the polycaprolactoneinclude SeRM super polymer SH3400P, SH2400P, and SH1310P available fromAdvanced Softmaterials Inc.

The hydroxyl group modified vinyl chloride-vinyl acetate copolymeradjusts the adhesion of the paint film while maintaining the scratchresistance of the paint film. The hydroxyl group modified vinylchloride-vinyl acetate copolymer is obtained, for example, by a methodof copolymerizing vinyl chloride, vinyl acetate and a monomer having ahydroxyl group (e.g., polyvinyl alcohol, hydroxyalkyl acrylate), or by amethod of partially or completely saponifying a vinyl chloride-vinylacetate copolymer.

The amount of the vinyl chloride component in the hydroxyl groupmodified vinyl chloride-vinyl acetate copolymer is preferably 1 mass %or more, more preferably 20 mass % or more, even more preferably 50 mass% or more, and is preferably 99 mass % or less, more preferably 95 mass% or less. Specific examples of the hydroxyl group modified vinylchloride-vinyl acetate copolymer include Solbin (registered trademark)A, Solbin AL, and Solbin TA3 available from Nissin Chemical IndustryCo., Ltd.

Preferable embodiments of the polyol composition are an embodimentcontaining a urethane polyol, wherein the urethane polyol includes apolyether diol having a number average molecular weight in a range offrom 600 to 3000 as a constituent component (first embodiment); and anembodiment containing a polyrotaxane, wherein the polyrotaxane has acyclodextrin, a linear molecule piercing through the cyclic structure ofthe cyclodextrin, and blocking groups located at both terminals of thelinear molecule to prevent disassociation of the cyclodextrin, and atleast a part of hydroxyl groups of the cyclodextrin is modified with acaprolactone chain via a —O—C₃H₆—O— group (second embodiment).

In the first embodiment, the amount of the urethane polyol in the polyolcomponent contained in the polyol composition is preferably 60 mass % ormore, more preferably 70 mass % or more, and even more preferably 80mass % or more. It is also preferable that the polyol compound of thepolyol composition according to the first embodiment consists of theurethane polyol.

In the second embodiment, the amount of the polyrotaxane in the polyolcomponent contained in the polyol composition is preferably 30 mass % ormore, more preferably 45 mass % or more, and even more preferably 60mass % or more, and is preferably 100 mass % or less, more preferably 90mass % or less, and even more preferably 85 mass % or less.

The polyol composition according to the second embodiment preferablycontains the polycaprolactone polyol. The mass ratio of thepolycaprolactone polyol to the polyrotaxane (polycaprolactonepolyol/polyrotaxane) is preferably 0/100 or more, more preferably 5/95or more, and even more preferably 10/90 or more, and is preferably 90/10or less, more preferably 85/15 or less, and even more preferably 80/20or less.

The polyol composition according to the second embodiment preferablycontains the hydroxyl group modified vinyl chloride-vinyl acetatecopolymer. The amount of the hydroxyl group modified vinylchloride-vinyl acetate copolymer in the polyol compound contained in thepolyol composition is preferably 4 mass % or more, more preferably 8mass % or more, and is preferably 50 mass % or less, more preferably 45mass % or less.

(Polyisocyanate Composition)

Examples of the polyisocyanate component of the polyisocyanatecomposition used in the present invention include a compound having atleast two isocyanate groups. Examples of the polyisocyanate include anaromatic polyisocyanate such as 2,4-tolylene diisocyanate, 2,6-tolylenediisocyanate, a mixture of 2,4-tolylene diisocyanate and 2,6-tolylenediisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI),1,5-naphthylene diisocyanate (NDI), 3,3′-bitolylene-4,4′-diisocyanate(TODD, xylylene diisocyanate (XDI), tetramethylxylylenediisocyanate(TMXDI), and para-phenylene diisocyanate (PPDI); an alicyclicpolyisocyanate or aliphatic polyisocyanate such as4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrogenatedxylylenediisocyanate (H₆XDI), hexamethylene diisocyanate (HDI),isophorone diisocyanate (IPDI), and norbornene diisocyanate (NBDI); andderivatives of these polyisocyanates. In the present invention, two ormore polyisocyanates may be used as the polyisocyanate.

Examples of the derivative of the polyisocyanate include anadduct-modified product obtained by a reaction between a diisocyanateand a polyhydric alcohol; an isocyanurate-modified product of adiisocyanate; a biuret-modified product of a diisocyanate; and anallophanate-modified product of a diisocyanate. The derivative of thepolyisocyanate from which free diisocyanate is removed is morepreferable.

The adduct-modified product is a polyisocyanate obtained by a reactionbetween a diisocyanate and a polyhydric alcohol. Preferable examples ofthe polyhydric alcohol include a low molecular weight triol such astrimethylolpropane and glycerin. As the adduct-modified product, forexample, an adduct-modified product of hexamethylene diisocyanate ispreferable, a triisocyanate (the following formula (1)) obtained by areaction between hexamethylene diisocyanate and trimethylolpropane; anda triisocyanate (the following formula (2)) obtained by a reactionbetween hexamethylene diisocyanate and glycerin are more preferable.

Examples of the isocyanurate-modified product include anisocyanurate-modified product of hexamethylene diisocyanate, and anisocyanurate-modified product of isophorone diisocyanate. A trimer ofhexamethylene diisocyanate (the following formula (3)) or a trimer ofisophorone diisocyanate is preferable.

Examples of the biuret-modified product include a trimerized product ofa diisocyanate, and a trimer of hexamethylene diisocyanate (thefollowing formula (4)) is preferable.

The allophanate-modified product is, for example, a triisocyanateobtained by further reacting a diisocyanate with a urethane bond formedby a reaction between a diisocyanate and a low molecular weight diol.

As the polyisocyanate component, the adduct-modified product ispreferable, the adduct-modified product (preferably a trimer) ofhexamethylene diisocyanate is more preferable. When the adduct-modifiedproduct of hexamethylene diisocyanate is used, the amount of theadduct-modified product of hexamethylene diisocyanate in thepolyisocyanate component is preferably 10 mass % or more, morepreferably 20 mass % or more, and even more preferably 30 mass % ormore. It is also preferable that the polyisocyanate component consistsof the adduct-modified product of hexamethylene diisocyanate.

In addition, as the polyisocyanate component, the isocyanurate-modifiedproduct is also preferable, the isocyanurate-modified product(preferably the trimer) of hexamethylene diisocyanate or theisocyanurate-modified product (preferably the trimer) of isophoronediisocyanate is more preferable, and a combination of theisocyanurate-modified product (preferably the trimer) of hexamethylenediisocyanate and the isocyanurate-modified product (preferably thetrimer) of isophorone diisocyanate is even more preferable. In the casethat the combination of the isocyanurate-modified product ofhexamethylene diisocyanate and the isocyanurate-modified product ofisophorone diisocyanate is used, the mass ratio (isocyanurate-modifiedproduct of hexamethylene diisocyanate/isocyanurate-modified product ofisophorone diisocyanate) of the isocyanurate-modified product ofhexamethylene diisocyanate to the isocyanurate-modified product ofisophorone diisocyanate is preferably 0.1 or more, more preferably 0.2or more, and even more preferably 0.3 or more, and is preferably 9 orless, more preferably 4 or less, and even more preferably 3 or less. Ifthe mass ratio falls within the above range, the spin rate on approachshots under a condition that there is grass between the golf ball andthe club face increases.

In addition, as the polyisocyanate component, it is preferable that theadduct-modified product and the isocyanurate-modified product are usedin combination, it is more preferable that the adduct-modified product(preferably the trimer) of hexamethylene diisocyanate and theisocyanurate-modified product (preferably the trimer) of hexamethylenediisocyanate are used in combination, or the adduct-modified product(preferably the trimer) of hexamethylene diisocyanate and theisocyanurate-modified product (preferably the trimer) of isophoronediisocyanate are used in combination. In this case, the mass ratio(adduct-modified product/isocyanurate-modified product) of theadduct-modified product to the isocyanurate-modified product ispreferably 0.1 or more, more preferably 0.2 or more, and even morepreferably 0.3 or more. If the mass ratio is 0.1 or more, the spin rateon approach shots under a condition that there is grass between the golfball and the club face further increases.

In addition, when the adduct-modified product of hexamethylenediisocyanate and the isocyanurate-modified product of hexamethylenediisocyanate are used as the polyisocyanate component, the total amountof the adduct-modified product of hexamethylene diisocyanate and theisocyanurate-modified product of hexamethylene diisocyanate in thepolyisocyanate component is preferably 70 mass % or more, morepreferably 80 mass % or more, and even more preferably 90 mass % ormore. It is also preferable that the polyisocyanate component consistsof the adduct-modified product of hexamethylene diisocyanate and theisocyanurate-modified product of hexamethylene diisocyanate.

In the case that the isocyanurate-modified product of hexamethylenediisocyanate and the isocyanurate-modified product of isophoronediisocyanate are used as the polyisocyanate component, the total amountof the isocyanurate-modified product of hexamethylene diisocyanate andthe isocyanurate-modified product of isophorone diisocyanate in thepolyisocyanate component is preferably 70 mass % or more, morepreferably 80 mass % or more, and even more preferably 90 mass % ormore. It is also preferable that the polyisocyanate component consistsof the isocyanurate-modified product of hexamethylene diisocyanate andthe isocyanurate-modified product of isophorone diisocyanate.

In the case that the adduct-modified product of hexamethylenediisocyanate and the isocyanurate-modified product of isophoronediisocyanate are used as the polyisocyanate component, the total amountof the adduct-modified product of hexamethylene diisocyanate and theisocyanurate-modified product of isophorone diisocyanate in thepolyisocyanate component is preferably 70 mass % or more, morepreferably 80 mass % or more, and even more preferably 90 mass % ormore. It is also preferable that the polyisocyanate component consistsof the adduct-modified product of hexamethylene diisocyanate and theisocyanurate-modified product of isophorone diisocyanate.

The amount (NCO %) of the isocyanate group of the polyisocyanatecomponent is preferably 0.5 mass % or more, more preferably 1.0 mass %or more, and even more preferably 2.0 mass % or more, and is preferably45 mass % or less, more preferably 40 mass % or less, and even morepreferably 35 mass % or less. It is noted that the amount (NCO %) of theisocyanate group of the polyisocyanate component can be represented by100×[mole number of isocyanate group in polyisocyanate×42 (molecularweight of NCO)]/[total mass (g) of polyisocyanate].

Specific examples of the polyisocyanate component include Burnock(Registered trademark) D-800, Burnock DN-950, and Burnock DN-955available from DIC corporation; Desmodur (Registered trademark)N75MPA/X, Desmodur N3300, Desmodur N3390, Desmodur L75 (C), and Sumidur(Registered trademark) E21-1 available from Sumika Bayer Urethane Co.,Ltd.; Coronate (Registered trademark) HX, Coronate HK, Coronate HL, andCoronate EH available from Tosoh Corporation; Duranate (Registeredtrademark) 24A-100, Duranate 21S-75E, Duranate TPA-100, DuranateTKA-100, and Duranate 24A-90CX available from Asahi Kasei ChemicalsCorporation; and VESTANAT (Registered trademark) T1890 available fromDegussa Co., Ltd.

In the curing reaction of the curing type paint composition, the molarratio (NCO group/OH group) of the isocyanate group (NCO group) includedin the polyisocyanate composition to the hydroxyl group (OH group)included in the polyol composition is preferably 0.1 or more, morepreferably 0.2 or more. If the molar ratio (NCO group/OH group) is lessthan 0.1, the curing reaction is insufficient. In addition, if the molarratio (NCO group/OH group) is excessively large, the amount of theisocyanate group is excessive, and the obtained paint film does not onlybecome hard and fragile but also has deteriorated poor appearance. Thus,the molar ratio (NCO group/OH group) is preferably 1.5 or less, morepreferably 1.4 or less, and even more preferably 1.3 or less. It isnoted that the reason why the appearance of the obtained paint filmdeteriorates if the amount of the isocyanate group in the paint becomesexcessive is that an excessive amount of the isocyanate group maypromote a reaction between the moisture in air and the isocyanate group,thereby generating a lot of carbon dioxide gas.

When the polyol composition according to the first embodiment is used asthe polyol composition, the polyisocyanate composition preferablycontains the biuret-modified product of hexamethylene diisocyanate, theisocyanurate-modified product of hexamethylene diisocyanate and theisocyanurate-modified product of isophorone diisocyanate. When thebiuret-modified product and isocyanurate-modified product ofhexamethylene diisocyanate are used in combination, the mixing ratio(biuret-modified product/isocyanurate-modified product) preferablyranges from 20/40 to 40/20, more preferably ranges from 25/35 to 35/25in a mass ratio.

When the polyol composition according to the second embodiment is usedas the polyol composition, the polyisocyanate composition preferablycontains at least one member selected from the group consisting of theadduct-modified product of hexamethylene diisocyanate, theisocyanurate-modified product of hexamethylene diisocyanate, and theisocyanurate-modified product of isophorone diisocyanate.

The paint may be either a waterborne paint mainly containing water as adispersion medium or a solvent-based paint mainly containing an organicsolvent as a dispersion medium, but is preferably the solvent-basedpaint. In the case of the solvent-based paint, examples of thepreferable solvent include toluene, isopropyl alcohol, xylene,methylethyl ketone, methylisobutyl ketone, ethylene glycol monomethylether, ethylbenzene, propylene glycol monomethyl ether, isobutylalcohol, and ethyl acetate. It is noted that the solvent may be added ineither of the polyol composition and the polyisocyanate composition, andin light of uniformly performing the curing reaction, the solvent ispreferably added in the polyol composition and the polyisocyanatecomposition, respectively.

The paint preferably further contains a modified silicone. If themodified silicone is contained as a leveling agent, unevenness of thecoated surface can be reduced, and thus a smooth coated surface can beformed on the surface of the golf ball. Examples of the modifiedsilicone include a modified silicone having an organic group beingintroduced to a side chain or terminal of a polysiloxane skeleton, apolysiloxane block copolymer obtained by copolymerizing a polyetherblock and/or a polycaprolactone block, etc. with a polysiloxane block,and a modified silicone having an organic group being introduced to aside chain or terminal of a polysiloxane block copolymer. Thepolysiloxane skeleton or the polysiloxane block is preferably linear,and examples thereof include dimethyl polysiloxane, methylphenylpolysiloxane, and methyl hydrogen polysiloxane. Examples of the organicgroup include an amino group, epoxy group, mercapto group, and carbinolgroup. In the present invention, as the modified silicone oil, apolydimethylsiloxane-polycaprolactone block copolymer is preferablyused, and a terminal carbinol modifiedpolydimethylsiloxane-polycaprolactone block copolymer is more preferablyused. This is because these block copolymers have excellentcompatibility with the caprolactone modified polyrotaxane and thepolycaprolactone polyol. Specific examples of the modified silicone usedin the present invention include DBL-C31, DBE-224, and DCE-7521available from Gelest, Inc.

The modified silicone remains in the paint film formed from the paintcomposition. The amount of the modified silicone in the paint film andin the curing type paint composition is preferably 0.01 part by mass ormore, more preferably 0.05 part by mass or more, and is preferably 10parts by mass or less, more preferably 5 part by mass or less, withrespect to 100 parts by mass of the base resin component constitutingthe outermost layer of the paint film.

In the curing reaction, a conventional catalyst may be used. Examples ofthe catalyst include a monoamine such as triethyl amine andN,N-dimethylcyclohexylamine; a polyamine such asN,N,N′,N′-tetramethylethylene diamine andN,N,N′,N″,N″-pentamethyldiethylene triamine; a cyclic diamine such as1,8-diazabicyclo[5.4.0]-7-undecene (DBU) and triethylene diamine; and atin catalyst such as dibutyltin dilaurate and dibutyltin diacetate.These catalysts may be used solely, or two or more of the catalysts maybe used in combination. Among them, the tin catalyst such as dibutyltindilaurate and dibutyltin diacetate is preferable, and dibutyltindilaurate is particularly preferable.

The paint film may further contain additives generally contained in apaint for a golf ball, such as an ultraviolet absorber, an antioxidant,a light stabilizer, a fluorescent brightener, an anti-blocking agent, aleveling agent, a slip agent, and a viscosity modifier, where necessary.

In the case of a multiple layered paint film, examples of the base resinconstituting the layer of the paint film other than the outermost layerof the paint film include a urethane resin, an epoxy resin, an acrylicresin, a vinyl acetate resin, and a polyester resin, and among them, theurethane resin is preferable. The layer of the paint film other than theoutermost layer of the paint film may be formed from a paint same as ordifferent from the paint for forming the outermost layer of the paintfilm.

(Golf Ball)

The golf ball according to the present invention is not particularlylimited, as long as the golf ball comprises a golf ball body and a paintfilm composed of at least one layer and formed on a surface of the golfball body. The construction of the golf ball body is not particularlylimited, and the golf ball body may be a one-piece golf ball, atwo-piece golf ball, a multi-piece golf ball such as a golf ballcomposed of three or more pieces, or a wound golf ball. The presentinvention can be applied appropriately to any one of the above golfballs.

(Core)

The one-piece golf ball body and the core used for a wound golf ball,two-piece golf ball and multi-piece golf ball will be explained.

The one-piece golf ball body or the core may be formed from aconventionally known rubber composition (hereinafter sometimes simplyreferred to as “core rubber composition”). For example, the one-piecegolf ball body or the core may be formed by heat pressing a rubbercomposition containing a base rubber, a co-crosslinking agent and acrosslinking initiator.

As the base rubber, particularly preferable is a high cis-polybutadienehaving a cis-bond in a proportion of 40 mass % or more, more preferably70 mass % or more, and even more preferably 90 mass % or more in view ofits advantageous resilience. As the co-crosslinking agent, anα,β-unsaturated carboxylic acid having 3 to 8 carbon atoms or a metalsalt thereof is preferable, and a metal salt of acrylic acid or a metalsalt of methacrylic acid is more preferable. As the metal constitutingthe metal salt, zinc, magnesium, calcium, aluminum or sodium ispreferable, and zinc is more preferable. The amount of theco-crosslinking agent is preferably 20 parts by mass or more and 50parts by mass or less with respect to 100 parts by mass of the baserubber. In the case that the α,β-unsaturated carboxylic acid having 3 to8 carbon atoms is used as the co-crosslinking agent, a metal compound(e.g. magnesium oxide) is preferably used. As the crosslinkinginitiator, an organic peroxide is preferably used. Specific examples ofthe organic peroxide include dicumyl peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. Amongthem, dicumyl peroxide is preferably used. The amount of thecrosslinking initiator is preferably 0.2 part by mass or more, morepreferably 0.3 part by mass or more, and is preferably 3 parts by massor less, more preferably 2 parts by mass or less, with respect to 100parts by mass of the base rubber.

In addition, the core rubber composition may further contain an organicsulfur compound. As the organic sulfur compound, diphenyl disulfides(e.g. diphenyl disulfide, bis(pentabromophenyl) disulfide), thiophenolsand thionaphthols (e.g. 2-thionaphthol) are preferably used. The amountof the organic sulfur compound is preferably 0.1 part by mass or more,more preferably 0.3 part by mass or more, and is preferably 5.0 parts bymass or less, more preferably 3.0 parts by mass or less, with respect to100 parts by mass of the base rubber. The core rubber composition mayfurther contain a carboxylic acid and/or a salt thereof. As thecarboxylic acid and/or the salt thereof, a carboxylic acid having 1 to30 carbon atoms and/or a salt thereof is preferable. As the carboxylicacid, an aliphatic carboxylic acid or an aromatic carboxylic acid (e.g.benzoic acid) may be used. The amount of the carboxylic acid and/or thesalt thereof is preferably 1 part by mass or more and 40 parts by massor less with respect to 100 parts by mass of the base rubber.

The core rubber composition may further appropriately contain a weightadjusting agent such as zinc oxide and barium sulfate, an antioxidant,or a colored powder, in addition to the base rubber, the co-crosslinkingagent, the crosslinking initiator, and the organic sulfur compound. Themolding conditions for heat pressing the core rubber composition may beappropriately set depending on the rubber formulation. Generally, theheat pressing is preferably carried out at 130° C. to 200° C. for 10 to60 minutes, or carried out in a two-step heating of heating at 130° C.to 150° C. for 20 to 40 minutes followed by heating at 160° C. to 180°C. for 5 to 15 minutes.

(Cover)

The golf ball body preferably comprises a core and a cover covering thecore. In this case, the hardness of the cover is preferably 60 or less,more preferably 55 or less, even more preferably 50 or less, and mostpreferably 45 or less in Shore D hardness. If the hardness of the coveris 60 or less in Shore D hardness, the spin rate is further increased.The lower limit of the hardness of the cover is not particularlylimited, and it is preferably 10, more preferably 15, and even morepreferably 20 in Shore D hardness. The hardness of the cover is a slabhardness of the cover composition molded into a sheet shape.

The thickness of the cover is preferably 0.1 mm or more, more preferably0.2 mm or more, and even more preferably 0.3 mm or more, and ispreferably 1.0 mm or less, more preferably 0.9 mm or less, and even morepreferably 0.8 mm or less. If the thickness of the cover is 0.1 mm ormore, the shot feeling of the golf ball is better, and if the thicknessof the cover is 1.0 mm or less, the resilience of the golf ball can bemaintained.

The resin component constituting the cover is not particularly limited,and examples thereof include various resins such as an ionomer resin, apolyester resin, a urethane resin and a polyamide resin; a thermoplasticpolyamide elastomer having a trade name of “Pebax (registered trademark)(e.g. “Pebax 2533”)” available from Arkema Inc.; a thermoplasticpolyester elastomer having a trade name of “Hytrel (registeredtrademark) (e.g. “Hytrel 3548” and “Hytrel 4047”)” available from DuPont-Toray Co., Ltd.; a thermoplastic polyurethane elastomer having atrade name of “Elastollan (registered trademark) (e.g. “ElastollanXNY97A”)” available from BASF Japan Ltd.; and a thermoplastic styreneelastomer having a trade name of “TEFABLOC” or thermoplastic polyesterelastomer available from Mitsubishi Chemical Corporation. These covermaterials may be used solely, or two or more of these cover materialsmay be used in combination.

Among them, the resin component constituting the cover is preferably thepolyurethane resin or the ionomer resin, particularly preferably thepolyurethane resin. When the resin component constituting the coverincludes the polyurethane resin, the amount of the polyurethane resin inthe resin component is preferably 50 mass % or more, more preferably 70mass % or more, and even more preferably 90 mass % or more. When theresin component constituting the cover includes the ionomer resin, theamount of the ionomer resin in the resin component is preferably 50 mass% or more, more preferably 70 mass % or more, and even more preferably90 mass % or more.

The polyurethane may be either a thermoplastic polyurethane or athermosetting polyurethane. The thermoplastic polyurethane is apolyurethane exhibiting plasticity by heating and generally means apolyurethane having a linear chain structure of a high-molecular weightto a certain extent. On the other hand, the thermosetting polyurethane(two-component curing type polyurethane) is a polyurethane obtained bypolymerization through a reaction between a low-molecular weighturethane prepolymer and a curing agent (chain extender) when molding thecover. The thermosetting polyurethane includes a polyurethane having alinear chain structure or a polyurethane having a three-dimensionalcrosslinked structure depending on the number of the functional group ofthe prepolymer or the curing agent (chain extender) to be used. As thepolyurethane, the thermoplastic elastomer is preferable.

The cover may further contain a pigment component such as a whitepigment (e.g. titanium oxide), a blue pigment and a red pigment, aweight adjusting agent such as calcium carbonate and barium sulfate, adispersant, an antioxidant, an ultraviolet absorber, a light stabilizer,a fluorescent material or a fluorescent brightener, or the like, inaddition to the above resin component, as long as they do not impair theperformance of the cover.

The method for molding the cover from the cover composition is notparticularly limited, and examples thereof include a method of injectionmolding the cover composition directly onto the core; and a method ofmolding the cover composition into hollow shells, covering the core witha plurality of the hollow shells and compression molding the core with aplurality of the hollow shells (preferably a method of molding the covercomposition into half hollow-shells, covering the core with two of thehalf hollow-shells and compression molding the core with two of the halfhollow-shells). The golf ball body having the cover formed thereon isejected from the mold, and as necessary, the golf ball body ispreferably subjected to surface treatments such as deburring, cleaning,and sandblast. In addition, if desired, a mark may also be formedthereon.

The total number of the dimples formed on the cover is preferably 200 ormore and 500 or less. If the total number of the dimples is less than200, the dimple effect is hardly obtained, and if the total number ofthe dimples exceeds 500, the dimple effect is hardly obtained becausethe size of the respective dimples is small. The shape (shape in a planview) of the dimples includes, for example, but is not limited to, acircle; a polygonal shape such as a roughly triangular shape, a roughlyquadrangular shape, a roughly pentagonal shape, and a roughly hexagonalshape; and other irregular shape. The shape of the dimples may beemployed solely, or two or more of the shapes may be employed incombination.

When the golf ball is a multi-piece golf ball such as a three-piece golfball, a four-piece golf ball and a golf ball composed of five or morepieces, examples of the material for forming the intermediate layerdisposed between the core and the outermost cover include athermoplastic resin such as a polyurethane resin, an ionomer resin, apolyamide resin, and a polyethylene; a thermoplastic elastomer such as astyrene elastomer, a polyolefin elastomer, a polyurethane elastomer, anda polyester elastomer; and a cured product of a rubber composition.Herein, examples of the ionomer resin include a product obtained byneutralizing at least a part of carboxyl groups of a copolymer composedof ethylene and an α,β-unsaturated carboxylic acid with a metal ion; anda product obtained by neutralizing at least a part of carboxyl groups ofa ternary copolymer composed of ethylene, an α,β-unsaturated carboxylicacid and an α,β-unsaturated carboxylic acid ester with a metal ion. Theintermediate layer may further contain a weight adjusting agent such asbarium sulfate and tungsten, an antioxidant, a pigment, and the like. Itis noted that the intermediate layer is sometimes referred to as aninner cover or an outer core, depending on the construction of the golfball.

(Formation of Paint Film)

The paint film of the golf ball according to the present invention canbe formed by applying the paint on the surface of the golf ball body.The method of applying the paint is not particularly limited, aconventional method can be adopted, and examples thereof include a spraycoating and electrostatic coating.

In the case of performing the spray coating with an air gun, thepolyisocyanate composition and the polyol composition are fed withrespective pumps and continuously mixed with a line mixer located in thestream line just before the air gun, and the obtained mixture isair-sprayed. Alternatively, the polyol and the polyisocyanate areair-sprayed respectively with an air spray system provided with a devicefor controlling the mixing ratio thereof. The paint application may beconducted by spraying the paint one time or overspraying the paintmultiple times.

The paint applied on the golf ball body can be dried, for example, at atemperature in a range of from 30° C. to 70° C. for 1 hour to 24 hours,to form the paint film.

The golf ball according to the present invention comprises a paint filmcomposed of at least one layer and formed on the surface of the golfball body. In a case of a multiple layered paint film, the outermostlayer of the paint film located at the outermost layer of the golf ballcontains the porous filler. In a case of a single layered paint film,the single layered paint film is the outermost layer of the paint film,and the single layered outermost paint film contains the porous filler.

The thickness of the outermost layer of the paint film of the golf ballaccording to the present invention is preferably 5 μm or more, morepreferably 7 μm or more, and is preferably 40 μm or less, morepreferably 30 μm or less, and even more preferably 20 μm or less. If thethickness of the outermost layer of the paint film falls within theabove range, the appearance is better, the abrasion resistance of thegolf ball is better, and the approach performance is better.

In the case that the paint film of the golf ball according to thepresent invention has a multiple layered structure, the total thicknessof the paint film is preferably 5 μm or more, more preferably 7 μm ormore, and even more preferably 9 μm or more, and is preferably 50 μm orless, more preferably 45 μm or less, and even more preferably 40 μm orless. If the thickness is 5 μm or more, the spin rate on approach shotsincreases, and if the thickness is 50 μm or less, the spin rate ondriver shots can be suppressed.

The ratio (d/T) of the volume average particle size (d: μm) of theporous filler to the thickness (T: μm) of the outermost layer of thepaint film containing the porous filler is preferably 0.01 or more, morepreferably 0.05 or more, and even more preferably 0.1 or more, and ispreferably 2.0 or less, more preferably 1.5 or less, and even morepreferably 1.0 or less. If the ratio (d/T) is 0.01 or more, thewater-discharging effect is greater and thus the spin performance undera wet condition is further enhanced, and if the ratio (d/T) is 2.0 orless, the appearance is better and the stain attachment can bedecreased.

The whole particle of the porous filler may exist inside the outermostlayer of the paint film, or alternatively a part of the particle of theporous filler may be exposed on the surface of the outermost layer ofthe paint film. It is noted that it is preferable that the wholeparticle of the porous filler exists inside the outermost layer of thepaint film, i.e. the porous filler is not exposed on the surface of theoutermost layer of the paint film.

The water sliding angle of the surface of the outermost layer of thepaint film of the golf ball according to the present invention ispreferably less than 50°, more preferably 45° or less, and even morepreferably 40° or less. If the water sliding angle is less than 50°, thewater-discharging effect during the flight on a rainy day is greater.The lower limit of the water sliding angle is not particularly limited,but it is generally 10°. The sliding angle is a tilt angle at which aliquid begins to slide downward when a solid sample having a level solidsurface on which a static liquid exists, is slowly tilted.

The adhesion energy of the surface of the outermost layer of the paintfilm of the golf ball according to the present invention is preferablyless than 10 mJ/m², more preferably 9 mJ/m² or less, and even morepreferably 8 mJ/m² or less. If the adhesion energy is less than 10mJ/m², the water-discharging effect during the flight on a rainy day isgreater. The lower limit of the adhesion energy is not particularlylimited, but it is generally 4 mJ/m².

The dynamic friction coefficient of the outermost layer of the paintfilm of the golf ball according to the present invention is preferably0.65 or more, more preferably 0.68 or more, even more preferably 0.70 ormore, and most preferably 0.72 or more, and is preferably 1.3 or less,more preferably 1.2 or less, and even more preferably 1.1 or less. Ifthe dynamic friction coefficient is less than 0.65, the spin rate onapproach shots under a condition that there is grass between the golfball and the club face decreases, and if the dynamic frictioncoefficient is more than 1.3, the paint film is too tacky and thus stainis easily attached thereon.

The peak temperature of the loss tangent (tan δ) of the outermost layerof the paint film is preferably −40° C. or more, more preferably −30° C.or more, and even more preferably −20° C. or more, and is preferably 40°C. or less, more preferably 30° C. or less, and even more preferably 20°C. or less. If the peak temperature of the loss tangent (tan δ) is −40°C. or more, the paint film has low tackiness and thus is hard to bestained, and if the peak temperature of the loss tangent (tan δ) is 40°C. or less, the paint film has a larger dynamic friction coefficient andthus the spin rate on approach shots under a condition that there isgrass between the golf ball and the club face increases.

The loss modulus (E″) of the outermost layer of the paint film at thetemperature of 24° C. is preferably 0.1 MPa or more, more preferably 0.5MPa or more, and even more preferably 1.0 MPa or more, and is preferably80 MPa or less, more preferably 65 MPa or less, and even more preferably50 MPa or less. If the loss modulus (E″) is 0.1 MPa or more, the paintfilm has low tackiness and thus is hard to be stained, and if the lossmodulus (E″) is 80 MPa or less, the paint film has a larger dynamicfriction coefficient and thus the spin rate on approach shots under acondition that there is grass between the golf ball and the club faceincreases.

The 10% elastic modulus of the outermost layer of the paint film ispreferably 1 kgf/cm² (0.10 MPa) or more, more preferably 3 kgf/cm² (0.29MPa) or more, and even more preferably more than 10 kgf/cm² (0.98 MPa),and is preferably 50 kgf/cm² (4.9 MPa) or less, more preferably 40kgf/cm² (3.9 MPa) or less, and even more preferably 30 kgf/cm² (2.9 MPa)or less. If the 10% elastic modulus of the outermost layer of the paintfilm is 1 kgf/cm² or more, the paint film has low tackiness and thus ishard to be stained, and if the 10% elastic modulus of the outermostlayer of the paint film is 50 kgf/cm² or less, the paint film has alarger dynamic friction coefficient and thus the spin rate on approachshots under a condition that there is grass between the golf ball andthe club face increases.

The dynamic friction coefficient, water sliding angle, adhesion energy,10% elastic modulus, and peak temperature of loss tangent of theoutermost layer of the paint film are controlled by the type and amountof the resin component, porous filler, etc. in the paint film.

The golf ball according to the present invention preferably has adiameter in a range from 40 mm to 45 mm. In light of satisfying theregulation of US Golf Association (USGA), the diameter is particularlypreferably 42.67 mm or more. In light of prevention of air resistance,the diameter is more preferably 44 mm or less, even more preferably42.80 mm or less. In addition, the golf ball according to the presentinvention preferably has a mass of 40 g or more and 50 g or less. Inlight of obtaining greater inertia, the mass is more preferably 44 g ormore, even more preferably 45.00 g or more. In light of satisfying theregulation of USGA, the mass is particularly preferably 45.93 g or less.

When the golf ball according to the present invention has a diameter ina range from 40 mm to 45 mm, the compression deformation amount(shrinking amount along the compression direction) of the golf ball whenapplying a load from 98 N as an initial load to 1275 N as a final loadto the golf ball is preferably 2.0 mm or more, more preferably 2.2 mm ormore, and is preferably 4.0 mm or less, more preferably 3.5 mm or less.If the compression deformation amount is 2.0 mm or more, the golf ballis not excessively hard and thus the shot feeling thereof is better. Onthe other hand, if the compression deformation amount is 4.0 mm or less,the resilience is greater.

FIG. 1 is a partially cutaway cross-sectional view of a golf ball 1according to one embodiment of the present invention. FIG. 2 is aschematic enlarged view showing a part of the golf ball of FIG. 1 . Thegolf ball 1 comprises a spherical core 2, a cover 3 covering thespherical core 2, and a paint film 4 formed on a surface of the cover 3.The paint film 4 is an outermost layer of the paint film located at theoutermost layer of the golf ball. A plurality of dimples 31 are formedon the surface of the cover 3. Other portions than the dimples 31 on thesurface of the cover 3 are lands 32. The paint film 4 is single layered.The paint film 4 contains a base resin and a porous filler 5 containingSiO₂ in an amount of 50 mass % or more as a constituent component.Although the porous filler 5 exists inside the paint film 4 withoutbeing exposed on the paint film surface in FIG. 2 , the porous filler 5may be exposed on the paint film surface.

EXAMPLES

Next, the present invention will be described in detail by way ofexamples. However, the present invention is not limited to the examplesdescribed below. Various changes and modifications without departingfrom the spirit of the present invention are included in the scope ofthe present invention.

[Evaluation Method]

(1) Core Hardness (Shore C Hardness)

The hardness measured at the surface of the core was adopted as thesurface hardness of the core. In addition, the core was cut into twohemispheres and the hardness measured at the central point of theobtained cut plane was adopted as the center hardness of the core. Thehardness was measured with an automatic hardness tester (Digitest IIavailable from Bareiss company) using a detector of “Shore C”.

(2) Slab Hardness (Shore D Hardness)

Sheets with a thickness of about 2 mm were produced by injection moldingthe intermediate layer composition or the cover composition. The sheetswere stored at 23° C. for two weeks. At least three of these sheets werestacked on one another so as not to be affected by the measuringsubstrate on which the sheets were placed, and the hardness of the stackwas measured with an automatic hardness tester (Digitest II availablefrom Bareiss company) using a detector of “Shore D”.

(3) Compression Deformation Amount (mm)

The deformation amount of the core along the compression direction(shrinking amount of the core along the compression direction), whenapplying a load from 98 N as an initial load to 1275 N as a final loadto the core, was measured.

(4) Thickness of Paint Film (μm)

The golf ball was cut into two hemispheres, and the cross section of thepaint film on the hemisphere was observed with a microscope (VHX-1000available from Keyence Corporation) to obtain the thickness of the paintfilm.

The measuring location of the film thickness will be explained byreference to FIG. 3, 4 . FIG. 3 is a schematic figure of a cross sectionof a golf ball. As shown in FIG. 3 , on the cross section of the golfball, a straight line A passing a central point of the ball and a bottomof any dimple, a straight line B perpendicular to the straight line A,and a straight line C having an angle of 45° with the straight line Aare prepared, and intersection points of these straight lines with thepaint film surface are adopted as a pole P, an equator E and a shoulderS, respectively.

FIG. 4 is a schematic figure of a cross section passing a bottom De of adimple 31 and a central point of a golf ball 1. The bottom De of thedimple 31 is the deepest location of the dimple 31. An edge Ed is apoint of tangency of the dimple 31 with a tangent T, wherein the tangentT is drawn by connecting both sides of the dimple 31. A measuringlocation Y on an inclined plane is a point at which a perpendicular lineintersects with the inclined plane of the dimple, wherein theperpendicular line is drawn from a midpoint of a straight lineconnecting the bottom De of the dimple and the edge Ed downward to thedimple 31. A measuring location X on a land is a midpoint between edgesof adjacent dimples. It is noted that in the case that adjacent dimplescontact each other so that no land exists, or in the case that the landis so narrow that the thickness is hard to be measured, the bottom, edgeor inclined plane of the dimple is adopted as the measuring point.

In the measurement, test samples of six balls from three locations, i.e.the dimple where the pole P exists, the dimple near the equator E andthe dimple near the shoulder S, were firstly prepared. Next, regardingeach test piece (dimple), the thickness of the paint film at the bottomDe, edge Ed, inclined plane Y and land X of the dimple was measured.Finally, measuring values of six balls were averaged, and the obtainedaverage value was adopted as the thickness of the paint film.

(5) Sliding Angle

The sliding angles of the golf ball surface and sheet having the paintfilm formed thereon were measured.

A measuring sample sheet was prepared by forming the paint film on aslab formed from the cover composition. Specifically, pellets of thecover composition were fully filled into a mold having a thickness of 2mm, and compression molded at 170° C. for 5 minutes. After being cooled,the slab was ejected from the mold. The surface of the slab was treatedwith sandblast. After that, a spray coating method using an air gun wasused to apply the paint such that the dried paint film had a desiredthickness.

The sliding angle was measured with a sliding contact angle meter(DMo-501SA available from Kyowa Interface Science, Inc.). The measuringconditions were as follows. In the measurement for the golf ball, waterwas dripped at the center of the dimple having a maximum diameter.

-   -   Measuring method: sliding method    -   Analysis method: curve fitting method (section: 60 dots)    -   Field of view: WIDE1    -   Water amount: 19±1 μL (needle being used: stainless steel needle        15G)    -   Sliding condition: 0 to 90° (2.0° per second, continuous        tilting)    -   Sliding and moving decision distance: tilt angle when moving at        least 3 dots

In addition, the adhesion energy (mJ/m²) was calculated from themeasuring values of the golf ball, using the following formula. It isnoted that r is a contact radius, w is a droplet mass, g isgravitational acceleration, and a is a sliding angle.Adhesion energy=(w×g×sin α)/(2×π×r)(6) Loss Tangent (tan δ)

The storage modulus E′ (Pa), loss modulus E″ (Pa) and loss tangent (tanδ) of the paint film were measured under the following conditions.

Apparatus: Dynamic viscoelasticity measuring apparatus (Rheogel-E4000available from UBM CO., Ltd.)

Test sample: A paint obtained by blending the polyisocyanate compositionand the polyol composition was dried and cured at the temperature of 40°C. for 4 hours to prepare a paint film having a thickness ranging from0.11 mm to 0.14 mm. The paint film was cut to prepare a test piecehaving a width of 4 mm and a distance between the clamps of 20 mm.

-   -   Measuring mode: tensile mode    -   Measuring temperature: −100° C. to 150° C.    -   Temperature increase rate: 4° C./min    -   Measuring date capturing interval: 4° C.    -   Oscillation frequency: 10 Hz    -   Measuring strain: 0.1%        (7) 10% Elastic Modulus of Paint Film

The tensile properties of the paint film were measured according to JISK7161 (2014). Specifically, the polyisocyanate composition and thepolyol composition were blended to prepare a paint, and the obtainedpaint was dried and cured at the temperature of 40° C. for 4 hours toprepare a paint film (thickness: 0.05 mm). The paint film was punchedinto the test piece type II (width of parallel part: 10 mm, gaugelength: 50 mm) prescribed in JIS K7127 (1999), to prepare a test piece.The tensile test of the test piece was conducted with a precisionuniversal tester (Autograph (registered trademark) available fromShimadzu Corporation) under testing conditions of a length betweengrips: 100 mm, a tensile speed: 50 mm/min and a testing temperature: 23°C., and the tensile stress at 10% strain (10% elastic modulus) wasrecorded.

(8) Dynamic Friction Coefficient

The dynamic friction coefficient of the golf ball was measured under thefollowing conditions. It is noted that in the following conditions, theload is small and the moving speed is low, thus the dynamic frictioncoefficient of the outermost paint film layer can be measured.

-   -   Tester: Tribo Master TL201TS (available from Trinity-Lab Inc.)    -   Test sample: golf ball    -   Face plate: A plate made of stainless steel (HT1770 (size: 50        mm×150 mm×thickness 2 mm) available from Nippon Steel Nisshin        Co., Ltd.) and having a face surface with an arithmetic mean        roughness Ra of 2.9 μm and a maximum height mean value Ry of        21.7 μm was used.    -   Preparation method of face plate: The face plate was obtained by        performing an air-blast treatment to the stainless steel. As the        grinding material, a mixture of alumina powder (#60) and steel        ball (ES300 available from Ervin industries Co., Ltd.) in a        mixing ratio of 1:1 was used. The blasting conditions were: a        distance of 10 cm between the face plate and the nozzle, and a        pressure of 4 to 6 kg/cm² just before the nozzle.    -   Measuring method of Ra and Ry: Ra and Ry were measured with a        surface roughness tester (SJ-301 available from Mitutoyo        Corporation) by a method based on JIS B 0601-1994. Ra, Ry were        each an average value of the values obtained at six measuring        points. In addition, the cutoff value λc was 2.5 mm.    -   Temperature: 23° C.    -   Ball moving speed: 2 mm/s    -   Load: 1.96 N (200 gf)    -   Measurement method: The ball was fixed with a chuck, and allowed        to move at a predetermined speed on a flat plate in a state that        200 gf of a load was applied on the ball, to measure the dynamic        friction force.    -   Measuring item: dynamic friction (average value in the section        of from 2-10 mm)        (9) Spin Rate Under a Dry Condition and Spin Rate Under a Wet        Condition

A sand wedge (trade name: “CG 15 forged wedge”, loft angel: 58°,available from Cleveland Golf Inc.) was installed on a swing machineavailable from Golf Laboratories, Inc. The golf ball was hit at a headspeed of 16 m/s, and the spin rate (rpm) thereof was measured bycontinuously taking a sequence of photographs of the hit golf ball. Themeasurement was conducted ten times for each golf ball, and the averagevalue thereof was adopted as the spin rate. The spin rate under the wetcondition was measured when the club face and the golf ball were in astate of being wet with water. It is noted that the spin rate of thegolf ball No. 10 was defined as 100, and the spin performance of eachgolf ball was represented by converting the spin rate of each golf ballinto this index.

(10) Spin Rate Under a Condition that there is Grass Between the GolfBall and the Club Face

A sand wedge (trade name: “CG 15 forged wedge”, loft angel: 58°,available from Cleveland Golf Inc.) was installed on a swing machineavailable from Golf Laboratories, Inc. The golf ball was hit at a headspeed of 16 m/s, and the spin rate (rpm) thereof was measured bycontinuously taking a sequence of photographs of the hit golf ball. Itis noted that two leaves (length: about 3 cm) of a wild grass wereattached to the golf ball that was the testing object, and the golf ballwas hit such that there existed the wild grass between the club face andthe golf ball. The measurement was conducted ten times for each golfball, and the average value thereof was adopted as the spin rate. It isnoted that the spin rate of the golf ball No. 10 was defined as 100, andthe spin performance of each golf ball was represented by converting thespin rate of each golf ball into this index.

1. Production of Spherical Core

According to the formulation shown in Table 1, the rubber compositionwas kneaded, and heat-pressed at the temperature of 150° C. for 19 min.in upper and lower molds, each having a hemispherical cavity, to obtaina spherical core having a diameter of 39.7 mm. It is noted that theamount of barium sulfate was adjusted such that the ball had a mass of45.6 g.

TABLE 1 Spherical core Rubber Polybutadiene rubber 100 composition Zincacrylate 30.5 formulation Zinc oxide 10 (parts Barium sulfateAppropriate by mass) amount Bis(pentabromophenyl) disulfide 0.3 Dicumylperoxide 0.7 Benzoic acid 2 Molding Temperature (° C.) 150 conditionTime (min) 19 Core Compression deformation amount (mm) 3.3 propertiesCenter hardness (Shore C) 53 Surface hardness (Shore C) 80 Hardnessdifference (Surface − center) 27 (Shore C) Polybutadiene rubber: “BR730(high-cis polybutadiene)” available from JSR Corporation Zinc acrylate:“ZN-DA90S” available from Nihon Jyoryu Kogyo Co., Ltd. Zinc oxide:“Ginrei R” available from Toho Zinc Co., Ltd. Barium sulfate: “BariumSulfate BD” available from Sakai Chemical Industry Co., Ltd.Bis(pentabromophenyl)disulfide: available from Kawaguchi ChemicalIndustry Co., Ltd. Dicumyl peroxide: “Percumyl (register trademark) D”available from NOF Corporation Benzoic acid: available from EmeraldKalama Chemical Co., Ltd.2. Preparation of Intermediate Layer Composition and Cover Composition

According to the formulations shown in Tables 2 and 3, the materialswere mixed with a twin-screw kneading extruder to prepare theintermediate layer composition and the cover composition in a pelletform. The extruding conditions were a screw diameter of 45 mm, a screwrotational speed of 200 rpm, and a screw L/D=35, and the mixture washeated to 160° C. to 230° C. at the die position of the extruder.

TABLE 2 Intermediate layer composition Himilan AM7329 55 Himilan 1555 45Barium sulfate Appropriate amount Titanium dioxide  3 Slab hardness(Shore D) 62 Himilan (registered trademark) AM7329: zinc ion-neutralizedethylene-methacrylic acid copolymer ionomer resin available from DuPont-Mitsui Polychemicals Co., Ltd. Himilan 1555: sodium ion-neutralizedethylene-methacrylic acid copolymer ionomer resin available from DuPont-Mitsui Polychemicals Co., Ltd.

TABLE 3 Cover composition Elastollan NY80A 100 Titanium dioxide 4Ultramarine blue 0.04 Slab hardness (Shore D) 27 Elastollan NY80A:thermoplastic polyurethane elastomer available from BASF Japan Ltd.3. Molding of Intermediate Layer

The intermediate layer composition obtained above was directly injectionmolded onto the spherical core obtained above to form the intermediatelayer (thickness: 1.0 mm) covering the spherical core.

4. Production of Reinforcing Layer

A reinforcing layer composition (trade name “Polin (registeredtrademark) 750LE” available from Shinto Paint Co., Ltd.) having atwo-component curing type epoxy resin as the base resin was prepared.The base agent contains a bisphenol A type solid epoxy resin in anamount of 30 parts by mass, and a solvent in an amount of 70 parts bymass. The curing agent contains a modified polyamide amine in an amountof 40 parts by mass, titanium dioxide in an amount of 5 parts by mass,and a solvent in an amount of 55 parts by mass. The mass ratio of thebase agent to the curing agent was 1/1. The reinforcing layercomposition was applied to the surface of the intermediate layer with anair gun, and kept for 12 hours in an atmosphere of 23° C., to form thereinforcing layer. The thickness of the reinforcing layer was 7 μm.

5. Molding of Cover

The cover composition in the pellet form was charged into each of thedepressed part of the lower mold for molding half shells, and a pressurewas applied to mold half shells. The spherical body having thereinforcing layer formed thereon was concentrically covered with two ofthe half shells. The spherical body and the half shells were chargedinto a final mold provided with a plurality of pimples on the cavitysurface. The cover (thickness: 0.5 mm) was formed by compression moldingto obtain golf ball bodies. A plurality of dimples having an invertedshape of the pimples were formed on the cover.

6. Preparation of Paint

Preparation of Polyol Compositions No. 1 to 3 (Polyrotaxane Composition)

According to Tables 4 and 5, as the resin component, a polyrotaxane(“SeRM (registered trademark) super polymer SH3400P (a polyrotaxanehaving a cyclodextrin, at least a part of hydroxyl groups thereof beingmodified with a caprolactone chain via a —O—C₃H₆—O— group, a linearmolecule being polyethylene glycol, and a blocking group being anadamantyl group; molecular weight of linear molecule: 35,000, hydroxylvalue: 72 mg KOH/g, total molecular weight of polyrotaxane: 700,000 inweight average molecular weight)” available from Advanced SoftmaterialsInc.), a polycaprolactone polyol (“Placcel (registered trademark) 308”(hydroxyl value: 190 to 200 mgKOH/g) available from Daicel ChemicalIndustries, Ltd.), and a vinyl chloride-vinyl acetate-vinyl alcoholcopolymer (“Solbin (registered trademark) AL (hydroxyl value: 63.4 mgKOH/g)” available from Nissin Chemical Industry Co., Ltd.), wereweighed. In 100 parts by mass of the resin component, 0.01 part by massof dibutyltin dilaurate and 100 parts by mass of a solvent (a mixedsolvent of xylene/methylethyl ketone=70/30 (mass ratio)) were mixed, toprepare the polyol compositions No. 1 to 3. In the case that the fillerwas added, the filler was added in the polyol composition in an amountof 100 parts by mass relative to 100 parts by mass of the base resinconstituting the paint film.

TABLE 4 Golf ball No. 1 2 3 4 5 6 7 Paint Polyol composition No. 1 2 3 33 3 3 (parts by mass) Urethane polyol — — — — — — — Polyrotaxane 36 7050 50 50 50 50 Polycaprolactone polyol 35 17 28 28 28 28 28 Vinylchloride-vinyl 29 13 22 22 22 22 22 acetate-vinyl alcohol copolymerPolyisocyanate No. 1 1 1 1 2 1 3 composition Adduct-modified product ofHDI 100 100 100 1000 50 100 70 (parts by mass) Biuret-modified productof HDI — — — — — — — Isocyanurate-modified product of HDI — — — — 50 — —Isocyanurate-modified product of IPDI — — — — — — 30 Mixing ratio(NCO/OH molar ratio) 1.2/1.0 1.2/1.0 1.2/1.0 1.2/1.0 1.2/1.0 1.4/1.01.2/1.0 Filler Type Zeolite Zeolite Diatomite Zeolite Zeolite ZeoliteZeolite Character Porous Porous Porous Porous Porous Porous PorousAmount of SiO₂ (mass %) 69-70 69-70 69-70 80 69-70 69-70 69-70 Mixingamount (relative to base resin) 100 100 100 100 100 100 100 Paint filmThickness (μm) 10 10 10 10 10 10 10 Property of paint Sliding angle(sheet: 20 μl) 44 43 44 44 44 43 43 Ball Sliding angle (ball: 20 μl) 3840 38 38 38 40 40 Adhesion energy (mJ/m²) 8 8 8 8 8 8 8 Peak temperatureof loss tangent (tanδ) (° C.) −3 0 −3 −3 1 −4 49 10% Elastic modulus(kgf/cm²) 21 20 21 20 29 18 30 Dynamic friction coefficient of outermostlayer of paint film 0.92 0.91 0.873 0.873 0.83 0.89 0.72 Golf ball Spinrate under a dry condition (rpm) 101 99 100 100 100 100 101 index Spinrate under a condition that there is grass between the 123 127 123 123122 125 107 evaluation golf ball and the club face (rpm) Spin rate undera wet condition (16 m/s•58°) 118 118 118 114 123 114 132 Golf ball No. 89 10 11 12 13 14 Paint Polyol No. 3 3 4 4 4 4 4 composition Urethanepolyol — — 100 100 100 100 100 (parts by mass) Polyrotaxane 50 50 — — —— — Polycaprolactone polyol 28 28 — — — — — Vinyl chloride-vinylacetate-vinyl 22 22 — — — — — alcohol copolymer Polyisocyanate No. 1 4 51 5 5 1 composition Adduct-modified product of HDI 100 — — 100 — — 100(parts by mass) Biuret-modified product of HDI — — 30 — 30 30 —Isocyanurate-modified product of HDI — 70 30 — 30 30 —Isocyanurate-modified product of IPDI — 30 40 — 40 40 — Mixing ratio(NCO/OH molar ratio) 1.2/1.0 1.2/1.0 0.38/1.0 1.2/1.0 0.61/1.0 1.2/1.01.2/1.0 Filler Type Talc — — Talc — — — Character Non- — — Non- — — —porous porous Amount of SiO₂ (mass %) — — — — — — — Mixing amount(relative to base resin) 100 — — 100 — — — Paint film Thickness (μm) 1010 10 15 15 15 15 Property of paint Sliding angle (sheet: 20 μl) 50 6257 50 56 49 55 Ball Sliding angle (ball: 20 μl) 46 60 61 51 59 45 52Adhesion energy (mJ/m²) 9 13 13 9 12 9 9 Peak temperature of losstangent (tanδ) (° C.) −2 48 52 10 68 84 8 10% Elastic modulus (kgf/cm²)22 20 10 21 65 180 20 Dynamic friction coefficient of outermost layer ofpaint film 0.9 0.72 0.62 0.8 0.57 0.62 0.98 Golf ball Spin rate under adry condition (rpm) 101 101 100 99 101 99 99 index Spin rate under acondition that there is grass between the 120 107 100 123 93 87 123evaluation golf ball and the club face (rpm) Spin rate under a wetcondition (16 m/s•58°) 84 100 100 100 109 118 91 Diatomite: Diatomaceousearth

TABLE 5 Golf ball No. 15 16 17 18 19 Paint Polyol composition No. 3 3 33 3 (parts by mass) Urethane polyol — — — — — Polyrotaxane 50 50 50 5050 Polycaprolactone polyol 28 28 28 28 28 Vinyl chloride-vinyl 22 22 2222 22 acetate-vinyl alcohol copolymer Polyisocyanate No. 4 6 4 7 2composition Adduct-modified product of HDI — 30 — 30 50 (parts by mass)Biuret-modified product of HDI — — — — — Isocyanurate-modified productof HDI 70 — 70 70 50 Isocyanurate-modified product of IPDI 30 70 30 — —Mixing ratio (NCO/OH molar ratio) 1.2/1.0 1.2/1.0 1.2/1.0 1.2/1.01.2/1.0 Filler Type Zeolite Zeolite Zeolite Zeolite Zeolite CharacterPorous Porous Porous Porous Porous Amount of SiO₂ (mass %) 69-70 69-7069-70 69-70 69-70 Mixing amount (relative to base resin) 10 10 30 30 50Paint film Thickness (μm) 10 10 10 10 10 Property of paint Sliding angle(sheet: 20 μl) 44 43 42 42 41 Ball Sliding angle (ball: 20 μl) 40 39 3939 38 Adhesion energy (mJ/m²) 8 8 8 8 8 Peak temperature of loss tangent(tanδ) (° C.) 28 44 44 12 12 10% Elastic modulus (kgf/cm²) 16 18 17 1920 Dynamic friction coefficient of outermost layer of paint film 0.720.75 0.74 0.74 0.74 Golf ball Spin rate under a dry condition (rpm) 101101 101 100 101 index Spin rate under a condition that there is grassbetween the 110 113 117 117 117 evaluation golf ball and the club face(rpm) Spin rate under a wet condition (16 m/s•58°) 123 125 132 132 132Preparation of Polyol Composition No. 4

Polytetramethylene ether glycol (PTMG) and trimethylolpropane (TMP) weredissolved as the first polyol component in a solvent (toluene andmethylethyl ketone). Dibutyltin laurate was added as a catalyst into theabove prepared solution in an amount of 0.1 mass % with respect to thetotal base materials. While keeping the temperature of the polyolsolution at 80° C., isophorone diisocyanate (IPDI) was added dropwise asthe first polyisocyanate component to the polyol solution and mixed.After finishing the addition of isophorone diisocyanate, stirring wascontinued until the isocyanate group disappeared. Then, the reactionliquid was cooled to the room temperature to prepare the urethane polyol(solid component content: 30 mass %). The formulation and the like ofthe obtained urethane polyol are shown in Table 6. In the case that thefiller was added, the filler was added in the polyol composition in anamount of 100 parts by mass relative to 100 parts by mass of the baseresin constituting the paint film.

TABLE 6 Urethane polyol Component First polyol component PTMG TMP Firstpolyisocyanate component IPDI Number average molecular weight of PTMG650 TMP:PTMG (molar ratio) 1.87:1 Molar ratio (NCO/OH) of NCO group ofpolyisocyanate 0.6 component to OH group of polyol component Amount ofPTMG (mass %) 46.2 Hydroxyl value of solid component (mgKOH/g) 128.0Weight average molecular weight 7200Polyisocyanate Composition

The following polyisocyanates were used to prepare the polyisocyanatecompositions No. 1 to No. 7 according to the formulations shown inTables 4 and 5.

Adduct-modified product of HDI: adduct-modified product of hexamethylenediisocyanate (Duranate (registered trademark) E402-80B (NCO amount:7.3%) available from Asahi Kasei Chemicals Corporation)

Biuret-modified product of HDI: biuret-modified product of hexamethylenediisocyanate (Duranate (registered trademark) 21S-75E (NCO amount:15.5%) available from Asahi Kasei Chemicals Corporation)

Isocyanurate-modified product of HDI: isocyanurate-modified product ofhexamethylene diisocyanate (Duranate TKA-100 (NCO amount: 21.7%)available from Asahi Kasei Chemicals Corporation)

Isocyanurate-modified product of IPDI: isocyanurate-modified product ofisophorone diisocyanate (VESTANAT (registered trademark) T1890 (NCOamount: 12.0%) available from Degussa Co., Ltd.)

6. Formation of Paint Film

The polyol composition and the polyisocyanate composition were mixedaccording to the formulation shown in Tables 4 and 5 to prepare thepaint compositions. The surface of the golf ball bodies obtained abovewas treated with sandblast and marked. The paint was applied with aspray gun, and dried for 24 hours in an oven at the temperature of 40°C. to obtain golf balls having a diameter of 42.7 mm and a mass of 45.6g.

Filler

Diatomaceous earth: “Radiolite F” (volume average particle size: 7 μm,bulk density: 0.40 g/cm³) available from Showa Chemical Industry Co.,Ltd.

Zeolite: “Molecular sieve 13X POWDER” (volume median size: 8.7 μm, bulkdensity: 0.5 g/cm³) available from Union Showa K.K.

Talc: “P8” (volume average particle size: 3.3 μm, bulk density: 0.12g/cm³) available from Nippon Talc Co., Ltd.

The application of the paint was conducted as follows. The golf ballbody was placed in a rotating member provided with a prong, and therotating member was allowed to rotate at 300 rpm. The application of thepaint was conducted by spacing a spray distance (7 cm) between the airgun and the golf ball body, and moving the air gun in an up and downdirection. The painting interval in the overpainting operation was setto 1.0 second. The application of the paint was conducted under thespraying conditions of overpainting operation: twice, spraying airpressure: 0.15 MPa, compressed air tank pressure: 0.10 MPa, paintingtime per one application: one second, atmosphere temperature: 20° C. to27° C., and atmosphere humidity: 65% or less. Evaluation resultsregarding the spin performance of the obtained golf balls are shown inTables 4 and 5.

It is apparent from Tables 4 and 5 that the golf ball according to thepresent invention wherein an outermost layer of the paint film locatedat the outermost layer of the golf ball contains a base resin and aporous filler, the base resin contains a polyurethane obtained by areaction between a polyisocyanate composition and a polyol composition,and the porous filler contains SiO₂ in an amount of 50 mass % or more asa constituent component, has excellent spin performance on approachshots under a wet condition and excellent spin performance on approachshots under a condition that there is grass between the golf ball andthe club face.

This application is based on Japanese patent application No. 2019-060595filed on Mar. 27, 2019 and Japanese patent application No. 2019-192019filed on Oct. 21, 2019, the contents of which are hereby incorporated byreference.

The invention claimed is:
 1. A golf ball comprising a golf ball body anda paint film composed of at least one layer and formed on a surface ofthe golf ball body, wherein an outermost layer of the paint film locatedat the outermost layer of the golf ball contains a base resin and aporous filler, the base resin contains a polyurethane obtained by areaction between a polyisocyanate composition and a polyol composition,the porous filler contains SiO₂ in an amount of 50 mass % or more and 95mass % or less as a constituent component, and the polyisocyanatecomposition contains, as a polyisocyanate component, an adduct-modifiedproduct of hexamethylene diisocyanate with an isocyanurate-modifiedproduct of hexamethylene diisocyanate, an adduct-modified product ofhexamethylene diisocyanate with an isocyanurate-modified product ofisophorone diisocyanate; or an isocyanurate-modified product ofhexamethylene diisocyanate with an isocyanurate-modified product ofisophorone diisocyanate.
 2. The golf ball according to claim 1, whereinthe polyol composition contains a polyrotaxane as a polyol component,the polyrotaxane has a cyclodextrin, a linear molecule piercing throughthe cyclic structure of the cyclodextrin, and blocking groups located atboth terminals of the linear molecule to prevent disassociation of thecyclodextrin, and at least a part of hydroxyl groups of the cyclodextrinis modified with a caprolactone chain via a —O—C₃H₆—O-group, and anamount of the polyrotaxane in the polyol component is 30 mass % or more.3. The golf ball according to claim 1, wherein the polyisocyanatecomposition contains the adduct-modified product of hexamethylenediisocyanate in an amount of 10 mass % or more in the polyisocyanatecomponent.
 4. The golf ball according to claim 1, wherein an amount ofthe porous filler is 3 parts by mass or more with respect to 100 partsby mass of the base resin.
 5. The golf ball according to claim 1,wherein the porous filler contains SiO₂ in an amount of 60 mass % ormore and 90 mass % or less as the constituent component.
 6. The golfball according to claim 1, wherein a surface of the outermost layer ofthe paint film has a water sliding angle of less than 50° and anadhesion energy of less than 10 mJ/m².
 7. The golf ball according toclaim 1, wherein the outermost layer of the paint film has a dynamicfriction coefficient of from 0.65 to 1.3 measured with a dynamicfriction tester under following conditions: <measurement conditions>moving speed: 2 mm/s load: 1.96 N measuring item: dynamic frictionaverage value in a moving distance of from 2 mm to 10 mm.
 8. The golfball according to claim 1, wherein the porous filler is at least onemember selected from the group consisting of diatomaceous earth, zeoliteand perlite.
 9. The golf ball according to claim 1, wherein the porousfiller has a volume average particle size of from 0.5 μm to 30 μm and abulk density of from 0.2 g/cm3 to 1.0 g/cm³.
 10. The golf ball accordingto claim 4, wherein the amount of the porous filler is 3 parts by massor more and 200 parts by mass or less with respect to 100 parts by massof the base resin.
 11. The golf ball according to claim 1, wherein thepolyol composition contains a urethane polyol as a polyol component, andthe urethane polyol includes a polyether diol having a number averagemolecular weight in a range of from 600 to 3000 as a constituentcomponent.
 12. The golf ball according to claim 2, wherein the polyolcomposition further contains a polycaprolactone polyol and/or a hydroxylgroup modified vinyl chloride-vinyl acetate copolymer as a polyolcomponent.
 13. The golf ball according to claim 12, wherein a mass ratio(polycaprolactone polyol/polyrotaxane) of the polycaprolactone polyol tothe polyrotaxane ranges from 0/100 to 90/10, and an amount of thehydroxyl group modified vinyl chloride-vinyl acetate copolymer in thepolyol component contained in the polyol composition ranges from 4 mass% to 50 mass %.
 14. A golf ball comprising a golf ball body and a paintfilm composed of at least one layer and formed on a surface of the golfball body, wherein an outermost layer of the paint film located at theoutermost layer of the golf ball contains a base resin and a porousfiller, the base resin contains a polyurethane obtained by a reactionbetween a polyisocyanate composition and a polyol composition, theporous filler contains SiO₂ in an amount of 50 mass % or more as aconstituent component, and an amount of the porous filler ranges from 30parts by mass to 200 parts by mass with respect to 100 parts by mass ofthe base resin.
 15. A golf ball comprising a golf ball body and a paintfilm composed of at least one layer and formed on a surface of the golfball body, wherein an outermost layer of the paint film located at theoutermost layer of the golf ball contains a base resin and a porousfiller, the base resin contains a polyurethane obtained by a reactionbetween a polyisocyanate composition and a polyol composition, theporous filler contains SiO₂ in an amount of 50 mass % or more and 95mass % or less as a constituent component, and the polyol compositioncontains a polyrotaxane or a urethane polyol as a polyol component,wherein the polyrotaxane has a cyclodextrin, a linear molecule piercingthrough the cyclic structure of the cyclodextrin, and blocking groupslocated at both terminals of the linear molecule to preventdisassociation of the cyclodextrin, and at least a part of hydroxylgroups of the cyclodextrin is modified with a caprolactone chain via a—O—C₃H₆—O— group, and an amount of the polyrotaxane in the polyolcomponent is 30 mass % or more; and the urethane polyol includes apolyether diol having a number average molecular weight in a range offrom 600 to 3000 as a constituent component.
 16. The golf ball accordingto claim 15, wherein the polyisocyanate composition contains anadduct-modified product of hexamethylene diisocyanate and anisocyanurate-modified product of hexamethylene diisocyanate as apolyisocyanate component.
 17. The golf ball according to claim 15,wherein the polyisocyanate composition contains an adduct-modifiedproduct of hexamethylene diisocyanate and an isocyanurate-modifiedproduct of isophorone diisocyanate as a polyisocyanate component. 18.The golf ball according to claim 15, wherein the polyisocyanatecomposition contains an isocyanurate-modified product of hexamethylenediisocyanate and an isocyanurate-modified product of isophoronediisocyanate as a polyisocyanate component.
 19. The golf ball accordingto claim 15, wherein the polyol composition contains the urethanepolyol, and the polyisocyanate composition contains a biuret-modifiedproduct of hexamethylene diisocyanate, an isocyanurate-modified productof hexamethylene diisocyanate and an isocyanurate-modified product ofisophorone diisocyanate, and a mass ratio (biuret-modifiedproduct/isocyanurate-modified product) of the biuret-modified product ofhexamethylene diisocyanate to the isocyanurate-modified product ofhexamethylene diisocyanate ranges from 20/40 to 40/20.
 20. The golf ballaccording to claim 15, wherein the polyol composition contains thepolyrotaxane, and the polyisocyanate composition contains at least onemember selected from the group consisting of an adduct-modified productof hexamethylene diisocyanate, an isocyanurate-modified product ofhexamethylene diisocyanate, and an isocyanurate-modified product ofisophorone diisocyanate.